cciss: change to discover first memory BAR

Add a method for discovering the first memory BAR.  All Smart Array
controllers to date have always had the the memory BAR as the first BAR.
A new controller to be released later this year breaks that model.

Signed-off-by: Mike Miller <mike.miller@hp.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>